Memory controllers are generally circuits dedicated to controlling and managing the flow of data written to and read from one or more memory devices. They may be suitably formed as separate devices or integrated with a central processing unit or other main controller, and serve the memory storage and access needs of various software application operations. Memory controllers implement the logic to read from and write to various types of memory devices, examples of which include dynamic random access memory (DRAM), as well as electrically programmable types of non-volatile memory such as flash memory, and the like.
To minimize the consequences of data corruption due to random sources of error, various error checking measures for detection and/or correction are employed in the art for the storage and retrieval of data from memory devices. One example of the various known measures is the use of an Error Correcting Code (ECC) feature for detection or correction of error in data words read from one or more memory devices. An ECC feature is usually used in memory controllers for computing devices that are particularly vulnerable to data corruption, or for computing devices involved in high data rate or other applications where substantial immunity to data corruption is particularly important. ECC features generally involve adding redundant ECC bits to a transmitted data segment (e.g., transmitted to a memory device) according to a predetermined code (of a selected ECC format). These ECC bits are of parity-type and permit the data segment to be properly recovered at the receiving end (by a receiving/recovery method suitably configured for the given ECC format), even if certain correctable errors were introduced in the transmission or storage of that data segment. The degree to which the errors are correctable would depend on the relevant properties of the particular code being used.
Memory controllers generally transmit, receive, and store data words, and a data word format may be defined by a multiple number of bytes. The multiple data bytes of each data word may be stored in a memory device formed by a plurality of integrated circuit chips, and each data byte may be stored in a different selectable chip of the memory device at the same relative address within each selectable chip.
Some memory controllers are configured for storage of such ECC-protected data according to a sideband ECC storage scheme (or format). A sideband scheme for storing ECC and data bits usually provides for an additional chip (e.g., an ECC chip) in which the ECC byte associated with a given data word's data bytes is exclusively stored. The data word's ECC byte is then stored much like its data bytes—at the same intra-chip address as those data bytes, but in its dedicated sideband ECC chip. For example, in some ECC-protected memory controller applications, a data word may be defined by 72 total bits, segmented into eight 8-bit data bytes and one 8-bit ECC byte (one ECC bit for each of the eight 8-bit data bytes). For such an example (a 72-bit data word formed by 8 data bytes plus 1 ECC byte), the data word is stored across nine selectable chips—eight selectable chips for the data bytes and one selectable chip for the associated ECC byte. Under the sideband ECC storage scheme, memory transactions for reading and writing data to and from memory devices contemplate and support sideband storage of ECC bytes with their associated data bytes (e.g., data words).
Other memory controllers may use a non-sideband ECC memory storage scheme, such as an ECC storage scheme (or format) where ECC-protected bytes are stored inline (along) with their ECC bytes in one or more of chips available on a given memory device. For example, under an inline ECC storage scheme, a portion of the memory storage locations available on a chip of a memory device may be allocated for primary data bytes and the remainder allocated for ECC bytes so that the ECC bytes are stored inline with the primary data bytes. Additionally, a memory controller implementing an inline ECC storage scheme may adapt a memory transaction for inline storage configurations, where different portions of given data words are stored at different intra-chip addresses. In this way, available memory device chips may be shared for data and ECC bit storage according to a wide range of memory space configurations depending on such factors as data word size, the number and layout of available storage cells, and the like. An inline ECC storage scheme may be utilized when ECC protection for memory transactions exists but a memory device is not adequately equipped or configured to support sideband storage of ECC bytes. For example, an inline ECC storage scheme (or feature) can provide ECC protection similar to a sideband ECC memory storage scheme without the sideband ECC memory storage scheme's need to widen the memory data path between a memory controller and a memory device to communicate ECC on dedicated pins alongside memory data (e.g., a 9-byte wide memory interface where 8 bytes of the memory are data and 1 byte is the ECC for the 8 bytes of data).